Malignant hyperthermia is an inherited skeletal muscle disorder of humans and pigs. The disease is characterized by an accelerated muscle metabolism, contracture development, and rapidly rising temperature in response to certain halogenated anesthetics. Once initiated, a vicious cycle is established and a fulminant syndrome evolves in which the body temperature may exceed 109.degree. F. The clinical picture is generally accompanied by muscle rigidity, tachychardia and other signs of circulatory and metabolic stress. The syndrome may progress directly to rigor and death from cardiovascular stress unless the malignant hyperthermia episode is recognized and treated promptly with the skeletal muscle relaxant, dantrolene. The reported incidence of malignant hyperthermia ranges from approximately 1 per 10,000 to 1 per 50,000 anesthetics, with an apparently higher incidence in children.
In addition to triggering malignant hyperthermia by halothane anesthetic, porcine malignant hyperthermia is also consistently triggered by excitement, apprehension, exercise, or environmental stress such as heat or hypoxia. Episodes of malignant hyperthermia in pigs yield inferior, pale, soft and exudative pork.
Active malignant hyperthermia results in a dramatic elevation of intracellular calcium in skeletal muscle fibers. The exact cause of the explosive rise in sarcoplasmic calcium is not completely understood. Several laboratories, however, have found that calcium release from malignant hyperthermia susceptible sarcoplasmic reticulum in skeletal muscle differs from that of normal sarcoplasmic reticulum in both isolated vesicles, as well as intact and skinned fibers. Consequently, the calcium release channel of the sarcoplasmic reticulum has been suspected of playing a significant role in malignant hyperthermia.
Evaluation of malignant hyperthermia susceptibility includes a history and physical examination for detection of subclinical symptoms. A geneology going back two generations with specific information about anesthetic exposure and agents will estimate the likelihood of exposure to triggering agents. Predisposition to the disease is also currently determined experimentally through a halothane and caffeine-induced contracture test on a skeletal muscle biopsy. This method, however, is time consuming, labor intensive and not always conclusive. A large biopsy sample is needed, the patient must be greater than 60 pounds for biopsy and the biopsy sample must be fresh. A quick, simple and accurate test for this disease would be immensely useful to physicians in identifying patients with susceptibility to malignant hyperthermia. The method would also provide swine breeders with a means of identifying animals susceptible to malignant hyperthermia attacks induced by stress before slaughter.